The present invention relates to a writing implement having a ball valve in a casing thereof so as to prevent a back flow of liquid to be applied and also to a fabricating method thereof.
Some of the conventional writing implements are provided with a mechanism for preventing ink (liquid to be applied) contained therein from flowing backward to bottom end thereof when a nib thereof is turned upward.
For example, Japanese Examined Utility Model Publication No. 4-52067 discloses a ball-point pen having therein projections extending axially and spaced apart radially and a ball seat formed more toward the bottom end than the projections. In this manner, a valve chamber is formed between the bearing and the projections and a ball valve member is accommodated loosely movably in the valve chamber. In this type of writing implements, if the nib is turned downward during the writing, the ball valve member comes to contact with the projections, thereby being preventing from moving toward a leading end and the ink flows to the nib through passages formed between the projections. If the nib is turned upward when the writing implement is not used for the writing, the ball valve member rests on the bearing to stop the ink flow, thereby preventing the back flow of ink toward the bottom end.
The writing implements described above meet with the following problems to be solved.
A) In a state where the nib is turned downward, i.e., where the ball valve member is engaged with the projections, it is necessary to cause a sufficient amount of ink to flow toward the nib through the passages between the ball valve member and the casing. Accordingly, the inside diameter of the valve chamber needs to be sufficiently greater than the outside diameter of the ball valve member. This allows the ball valve member to move freely in the valve chamber not only axially, but also radially. Because of this unnecessary movement, it takes a long time for the ball valve member to rest on the bearing when the nib is turned suddenly upward from a state where it faces downward and hence it is difficult to prevent the back flow of ink immediately. Further, in a state where the nib is turned not right upward, but obliquely upward, the ball valve member may not rest on the bearing exactly, thereby causing the back flow of ink to be prevented unsatisfactorily.
B) Since the movement of the ball valve member is stopped by the axially extending projections, a total contact area of the ball valve member with the projections is small. Thus, there is a demand for a structure capable of preventing more reliably the ball valve member from moving out of the valve chamber. If the contact area of the ball valve member with the projections is increased, i.e., the projections are made larger in the aforementioned structure, the ink passages formed between the projections are narrowed, thereby making it difficult to supply a sufficient amount of ink to the nib.